There are many industrial processes involving the heating of water to high temperatures. For example, in the oil industry, it is a conventional practice to generate steam and/or hot water from produced oil field waters and inject the resulting steam or water into a subterranean formation in the course of a thermal oil recovery procedure. Various other applications involve the generation of steam or hot water for heating or power generating purposes or in distillation techniques such as the conversion of brine to potable water. In many cases, the feed water is a hard water containing divalent metal ions which form water insoluble precipitates, commonly referred to as "scale." The presence of scale forming constituents in feed waters is particularly troublesome in steam generation plants in which scale deposits on heat exchange surfaces, pipes, etc. can accumulate very rapidly. Most steam generation techniques require the use of good quality feed water in order to prevent the formation of scale on heat exchange tubes and the like. Thus, it is a conventional practice to pretreat boiler feed waters and other waters to be heated by techniques such as filtration, ion exchange, flotation, sedimentation, and the like to remove dissolved and suspended solids.
The chemical reactions which result in the precipitation of scale forming compounds are accelerated by heat and in some cases this fact is utilized to advantage. For example, U.S. Pat. No. 3,510,796 to Hull discloses the heating of boiler feed water with steam to precipitate divalent metal ions as calcium carbonate, magnesium hydroxide, magnesium silicate, calcium sulfate, and barium sulfate.
Other techniques involve the use of solid, particulate heat exchange materials. For example, U.S. Pat. No. 3,242,975 to Kogan discloses a heat exchanger of the pebble type which is said to be particularly useful in the conversion of sea water to potable water. In this system, heat exchange particles or "pebbles" are heated in an upper pebble chamber and then passed downwardly into a second heating chamber where they move in countercurrent flow with a cold brine which is introduced into the heating chamber at the bottom thereof. The heat loss from the hot pellets heats the brine to a suitable temperature; e.g., 215.degree. F. The now relatively cool pebbles are withdrawn from the heating chamber and conveyed by means of an elevator conveyor upwardly to the first pebble chamber where they are reheated.
Other water heating techniques involving the use of hot particulate materials are disclosed in U.S. Pat. Nos. 3,335,083 and 3,376,204 to Tidball. In these procedures, a liquified heat-transfer medium such as molten metal is passed from a sparger located in the upper portion of a heating chamber through which water containing scale forming constituents is passed. As the molten metal contacts the water, it is solidifed to form shot particles which then move downwardly to the bottom of the chamber where they are collected. The aqueous liquid in the chamber is heated to a temperature of about 250.degree. F. or higher to promote the reactions leading to the precipitation of the divalent metal ions which scale deposits. The scale precipitates tend to form on the shot particles as they fall through the water. The shot and scale deposits are removed from the heating chamber into a reservoir where the shot particles are heated to a temperature above their melting point. During this procedure the less dense scale forms a layer on the molten metal from which it is recovered and passed to a suitable disposal facility. The remelted metal is circulated by means of a pump upwardly through a conduit to the sparger where it is reintroduced into the heating vessel.